Remove is-json package

package.json

@@ -50,7 +50,6 @@
     "is-eot": "1.0.0",
     "is-gif": "3.0.0",
     "is-jpg": "2.0.0",
-    "is-json": "2.0.1",
     "is-otf": "0.1.2",
     "is-png": "1.1.0",
     "is-svg": "3.0.0",